WASHINGTON // A National Security Agency analysis released yesterday
contends that an alleged 1964 attack on U.S. ships in the Gulf of Tonkin, which
the Johnson administration cited as justification for greater U.S. military
involvement in Vietnam, never happened, casting further doubt on the rationale
for escalation of the conflict.

The material posted on the Internet at midnight Wednesday included one of the
largest collections of secret intercepted communications ever made available
for study.

The most provocative document is a 2001 article in which an NSA historian argued
that the agency's intelligence officers "deliberately skewed" the
evidence passed on to policymakers on the crucial question of whether North
Vietnamese ships attacked U.S. destroyers on Aug. 4, 1964.

Based on the mistaken belief that such an attack had occurred, President Lyndon
B. Johnson ordered airstrikes on North Vietnam, and Congress passed a broad
resolution authorizing military action.

The historian, Robert J. Hanyok, wrote the article in an internal publication,
and it was classified as top secret despite the fact that it dealt with events
in 1964. Word of Hanyok's findings leaked to historians outside the agency,
who requested the article under the Freedom of Information Act in 2003.

Some intelligence officials said they believe the article's release was delayed
because the agency was wary of comparisons between the role of flawed intelligence
during the Vietnam War and that preceding the U.S.-led invasion of Iraq.

Hanyok declined to comment Wednesday. But Don Weber, an NSA spokesman, denied
that any political consideration was involved.

"There was never a decision not to release the history" written by
Hanyok, Weber said. On the contrary, he said, the release was delayed because
the NSA wanted to make public the raw material that Hanyok used for his research.

"The goal here is to allow people to wade through all that information
and draw their own conclusions," Weber said.

Thomas S. Blanton, director of the National Security Archive at George Washington
University, called the release of the document "terrific," noting
that the eavesdropping material known as signals intelligence, or SIGINT, is
the most secret information the government has.

"NSA may be the most close-mouthed of all U.S. government agencies,"
said Blanton, whose organization has published on the Web many collections of
previously secret documents. "The release of such a large amount of SIGINT
is unprecedented."

In his 2001 article, an elaborate piece of detective work, Hanyok wrote that
90 percent of the intercepts of North Vietnamese communications relevant to
the supposed Aug. 4, 1964, attack were omitted from the major agency documents
going to policymakers.

"The overwhelming body of reports, if used, would have told the story
that no attack had happened," he wrote. "So a conscious effort ensued
to demonstrate that an attack occurred."

Claims that North Vietnamese boats attacked two U.S. warships on Aug. 4 --
two days after an initial assault on one of the ships -- rallied Congress behind
Johnson's buildup of the war. The Gulf of Tonkin Resolution passed three days
later empowered him to take "all necessary steps" in the region and
opened the way for large-scale commitment of U.S. forces.

The Hanyok study does not necessarily reflect the agency's position.

"In truth, Hanoi's navy was engaged in nothing that night but the salvage
of two of the boats damaged on 2 August," Hanyok wrote.

He said that "the handful of SIGINT reports which suggested that an attack
had occurred contained severe analytical errors, unexplained translation changes,
and the conjunction of two unrelated messages into one translation. This latter
product would become the Johnson administration's main proof of the Aug. 4 attack."

Hanyok wrote that he did not find "manufactured evidence and collusion
at all levels"; rather, it appeared that intelligence-gatherers had made
a series of mistakes and that their superiors did not set the record straight.

Conflicting and confused reports from the scene have long cast doubt on whether
the events had unfolded as claimed.

Hanyok's analysis of previously top secret intelligence adds insight on North
Vietnam's communications from that time, showing, he said, that the supposed
attackers did not even know the location of the destroyers, the USS Maddox and
USS C. Turner Joy, as the two ships patrolled off the North Vietnamese coast.

A shorter agency study done years earlier and also released yesterday indicated
that the U.S. ships did not know what, if anything, was coming at them as they
zigzagged to evade what the crews feared were torpedoes and as they fired on
targets identified by radar.

That study concluded with a wry note saying that the destroyers resumed their
patrols after a heavy round of U.S. airstrikes on North Vietnamese ports, "and
the rest is just painful history."

A detailed chronology assembled days after the episode for the Joint Chiefs
of Staff by J.J. Merrick, commander of Destroyer Division 192, reflected the
uncertainty of that night.

It said that sonar in many cases picked up sounds that were believed to be
torpedoes but turned out to be "self noise," the beating of the ships'
own propellers, or noise from patrol boats or supporting planes that were strafing
the dark sea in cloudy skies, unable to see any prey.

In another instance, however, the report contended that a "torpedo wake
was seen by four people."

The Maddox had been fired on by North Vietnamese patrol boats Aug. 2, 1964,
suffering superficial damage.